OFDM and OFDMA wireless communication systems under IEEE 802.16 use a network of base stations to communicate with wireless devices (i.e., mobile stations) registered for services in the systems based on the orthogonality of frequencies of multiple subcarriers and can be implemented to achieve a number of technical advantages for wideband wireless communications, such as resistance to multipath fading and interference. Each base station (BS) emits and receives radio frequency (RF) signals that convey data to and from the mobile stations (MS). Such an RF signal from a BS includes an overhead load, in addition to the data load (voice and other data), for various communication management functions. Each MS processes the information in the overhead load of each received signal prior to processing the data.
Under the current versions of the IEEE 802.16 standard for the OFDMA systems, every downlink subframe from a base station includes a preamble and a frame control header (FCH) following the preamble as part of the overhead load. The preamble includes information for searching a cell and a cell sector within a cell and for synchronizing a mobile station in both time and frequency with the received downlink signal. The FCH portion of the downlink subframe includes 24 bits with information on the downlink transmission format (e.g., the downlink media access protocol, or DL MAP) and control information for the downlink data reception (e.g., allocation of the subcarriers in the current downlink frame). Therefore, a receiver, such as a MS, first decodes the FCH to determine the coding type and length of the DL MAP, decodes the corresponding DL MAP, and then extracts the data.
Because power consumption is a significant concern in mobile communication devices, mobile stations may enter a sleep or idle mode and power down certain subsystems after a certain period of inactivity. However, even when a mobile communication device is in a sleep or idle mode, it needs to periodically awake and decode frames in order to “listen” for particular power-save related messages, such as paging messages, traffic indication messages, downlink channel description (DCD) messages, and uplink channel description (UCD) messages.